Modern aircraft designs have included multi-control surface aircraft, such as the X-29 aircraft which employs a movable canard. Due to the location of the center of gravity of such an aircraft, there is inherent instability which must be carefully attended to by a computer-aided pilot flight control system. In conventional systems, feedback in the flight control system is provided with normal acceleration and pitch rate parameters, derived from gyros and accelerometers. This feedback data is supplied to a servo system which is intended to stabilize the aircraft.
In multi-control surface high performance aircraft such as the canard-equipped X-29, the craft is inherently unstable, and dependence upon conventional flight control system technology has raised the problems of stability margin and high control actuator noise. At high operational speeds, these factors detract from the effectiveness of such an aircraft.